Production of cup-shaped hollow bodies from metal billets



O April 8, 1941.

K. KoRBuLY 2,237,993

PRODUCTION OF CUP-SHAPED HOLLOW BODIES FROM METAL BILBETS k Filed April l5, 1959 Lw. W, Wm' im.

iftatcnted Apr. 8, 1941 PRODUCTION OF CUP-SHAPED HOLLOW BODIES FROM METAL BILLETS Karoly Korbuly, Csepel, Hungary, assignor to the irm Tube Industrial Participation Limited, Breganzona-Lugano, Switzerland, a. corporation of Switzerland Application April 15, 1939, Serial No. 268,131 In Hungary and Germany April 23, 193B Claims.

Cup-shaped metal bodies (i. e. tubular metal bodies closed at one end) such as are required in particular for further treatment in a drawingor extrusion bench, are generally produced by forcing a piercing mandrel into a glowing billet of the metal (especially iron or steel) while the billet is situated in a matrix which determines the external form of the hollow body.

.lis a prerequisite of the said further treatment is that the length of the hollow body shall be a multi-ple of its diameter, it inevitably happens that the mandrel in being forced into the billet becomes deflected to a greater or smaller extent out ci the axial direction, and that in conseuuence the walls of the hollow body and of the resulting tubular product are of irregular thickness. The risk of deflection of the mandrel increases with the length of the bore and the degree oi pressure required. This latter can be reduced by employing for the production of a round hollow body, an angular billet whose edges centre it in a circular matrix and by having the cross section oi the free space left between the matrix and the walls oi the billet as nearly as possible equal to the cross section oi the bore to be formed, so that, in the operation oi piercing, the metal undergoes substantially lateral displacement only with minimum tendency to flow in the longitudinal direction. However, in this manner only hol,

long piercing stroke have to be employed, this accordingly increasing the rish oi dedection. ci the mandrel. To overcome this drawback it has been. proposed (British Patent t'lldllii) to set a glowing metal billet d (see liig. i ot' the drawing accompanying this speciilcationl on a plunger c and torce the billet, after the manner oi an eutrusion press, between a mandrel b and a draw ing ring u tapering towards its enit, by which :means it was hoped to produce comparatively long hollow workpieces with accurately centred hores. lEiut in this procedure the considerable lateral displacement oi' the metal was necessarily accompanied by v eiitensive elongation which, owing to the very heavy pressure required, increased the diiculty of keeping the mandrel centred.

'l'he present invention remedies this detect, by iorclng the workpiece in opposite senses twice through the saine die. For this purpose, in the tiret stroke the total cross section oi the Workdii tid

pieces, bore included, is increased by forcing the metal of the glowing billet ln an extrusion press between a mandrel and a die Whose cross section widens towards the end facing. f

Thereupon the workpiece is forced in the opposite direction, in the same heat and with the aid of the same mandrel, through the die of the extrusion press, the workpiece being thereby reduced to the smallest diameter of the die and correspondingly elongated.

Owing to the described operation being distributed over two #strokes of the press, namely the piercing or pressing stroke and the drawing stroke, the piercing stroke and therefore the requisite pressure can be very small, so that the risk of deecting the mandrel is practically nonexistent. The drawing stroke, on the other hand, may be considerably longer, so that very' long workpieces can be produced-for example oi such a length that the 'hot workpiece issuing from the presscan be drawn, in the same heat, and in a single operation in a draw-bench, to the length oi an ordinary gas bottle or cylinder. The circumstance that the workpiece does not leave the die between the piercing strolre and the drawing stroke ensures the perfectly centred guidance oi the mandrel at the beginning oi the drawing stroke.

li the closed end oi the hollow body is to have a 'comparatively thin walled extension. (tor eri-D ample, ior the ioot oi a steel gas cylinder) or a pointed, solid headlong by comparison with the diameter (as is the case with hollow bodies tor the production oi hollow projectiles) correspond ing recesses must be provided in the end taco ot the' press ram. To facilitate the penetration oi the metal into these very deep and narrow ree cesses, the procedure employed in the or piercing stroke consists, in contrast to Patent No. 371,919, not in iorcing the mandrel and press cylinder on to the stationary rain oi the press but in iorcing the movable ram into the cylinder, which togetherl with the mandrel is stationary.

big. a oi the accompanying drawing is a dia grammatic longitudinal section oi a typical ern-- bodiment oi' a press according to the invention, ior the production oi hollow bodies ior use in making gas cylinders, the parts being shown in a position during the piercing stroke.

Fig. 3 shows the press during the drawing stroke.

l'ig. l shows a form ot the press tor producing hollow bodies for projectiles.

Mounted in the press trame l 'are the upright cylinder 2 of the extrusion press and the die 3 .'widening out towards the lower end. The ram 4 is vertically guided above the cylinder, and the mandrel 5 is similarly guided below the cylinder. Before and during the piercing of a billet 6 the mandrel 5 occupies the position shown in Fig. 2, i. e. the end of the mandrel lies between the outer and inner ends of the die 3 and therefore within the operative range of the latter. According to the invention, and in contrast to the known presses, the mouth of the outer end (facing the mandrel) of the die 3 is wider than that of the end remote from the mandrel. Preferably, the

inner profile of the die has a point of inflection In operation the ram 4 is raised high enough to allow a glowing billet 6 to be introduced into the cylinder 2 from above. The billet may completely iill the cross section of the cylinder, or merely touch the wall of the latter by means of guiding edges. The ram is now depressed, causing the metal of the billet to extrude between the stationary mandrel 5 and the die 3, the workpiece thereby assuming an annular cross section whose outer diameter exceeds the inside diameter of the press cylinder. At the same time, the workpiece pushes forward against the pressure of the spring 8 a centering slide l, which is guided between4 the mandrel 5 and the frame l. The piercing or pressing stroke terminates as soon as the ram 4 nears the die 3, and has, in the meantime, formed a bottom of the desired thickness and shape. Next the ram 4 is raised, and the mandrel 5 is forced upwards (either at the same time or after the raising of the ram) thereby forcing the workpiece in the reverse direction through the die 3 and without it having issued from the die. During this last recited step the die 3 acts as a drawing ring, which draws the short, thickwalled workpiece represented in Fig. 2 into the shape of a comparatively long and thin-walled hollow body represented in Fig. 3.

With the ram head shaped as in Fig. 2, the drawing -stroke according to Fig. 3 produces a hollow body which, in the same heat and after being forced through further dies or rolls, can be given in a single further operation the form of a finished gas cylinder, except for the operation of constricting the mouth opening of the latter. In contrast to the usual practice of subsequent shaping and shrinking-on, the bottom and foot of the cylinder, being formed integrally with th body, are perfectly reliable.

To enable the annular groove 9 (necessary for y shaping the foot of the gas cylinder) in the ram head to become completely fllledwith metal, al-l though said groove is Very narrow as compared with its depth, the press must be so designed that during the first or piercing stroke, At-he pressure must be applied to the work-piece by the vram 4 itself. The same arrangement is also necessary when, for the purpose of producing hollow bodies for conversion into hollow projectiles, the bottom is to have ythe form (Fig. 4) of a tip which is comparatively long in relation to the diameter of the hollow body.

By means of the above described method comparatively long cup-shaped hollow bodies with thin walls can be produced from steels (such as high-grade steels of high mechanical strength) that are difficult to work, thus enabling much thinner and lighter gas cylinderspfor example than heretofore to be obtained.

What I claim is:

l. A method of producing a cup-shaped hollow body from a metal billet in an extrusion press having a mandrel cooperating with a die with a tapered bore disposed in the mouth of the press, comprising the steps of forcing the heated billet between the mandrel and the die arranged with the larger end of its bore facing the mandrel, and then forcing the billet, in the same heat, through the die in `the reverse direction by means of the mandrel.

2. A method of producing a cup-shaped hollow body from a metal billet in an extrusion press having a mandrel cooperating with a die with a tapered bore, comprising the steps of holding the mandrel stationary with its working end adjacent the wider end of the tapered bore of the die, forcing the heated billet into the die at the smaller end of its bore until metal of the billet is extruded from the larger end of the bore and is penetrated bythe mandrel, and then forcing the billet in the same heat and in situ through the die in thet reverse direction by advancing said mandrel through the bore of the die and beyond the smaller end of the bore.

3. An extrusion press for making cup-shaped hollow bodies from metal billets, comprising an extrusion cylinder into which a billet can be introduced, a die with a tapered bore arranged at an end of the cylinder with the smaller end of the bore towards the cylinder, a ram reciprocating in said cylinder, and a mandrel reciprocable with a stroke longer than that of the ram., said mandrel being coaxial with said cylinder, movable through said bore from its larger end, and iixable in a position adjacent said larger end to form therewith an annular extrusion opening, said reciprocating mandrel having a diameter which is smaller than the diameter of the cylinder by the thickness of the hollow body. to be produced so that the stroke of the mandrel exy the glowing billet onto a mandrel pgrojecting .Y

into the mouth of an extrusion press, increasing the total cross-section of the workpiece by forcing the metal of the workpiece between the man- 

